Determination of Cleanup Criteria Due to Possible Radiological Hazard in Some Tantalite Mining Sites in Oke-Ogun, Oyo State, Nigeria

Artisanal mining of solid minerals exposes workers to ionizing radiation from naturally occurring radioactive materials (NORMs) present in ores. This study assessed radiological hazards of artisan miners and established clean-up criteria for the selected mining sites at Komu, Sepeteri, Gbedu, and Eluku mining sites in the Oke-Ogun region of Oyo State, Nigeria. Seventeen soil samples were randomly collected and analyzed for activity concentrations of radionuclides (226Ra, 238U, 232Th, and 40K) using a high-purity germanium gamma spectrometer. Residual radioactivity (RESRAD) 7.2 code software was used to determine the cleanup criteria and radiological risk, viz., the effective dose and cancer risk of miners for the sites. The activity concentrations (Bq/kg) ranged from 29 ± 5 to 261 ± 8 for ²²⁶Ra, from 1.03 ± 0.25 to 318.38 ± 121 for 232Th, from 66 ± 20 to 194 ± 61 for 238U, and from 71 ± 4 to 1708 ± 98 for ⁴⁰K. The RESRAD results showed that all sites exceeded the permissible limit, with the sum of the radionuclide activity concentration fractions in the soil ranging from 1.48 to 7.16 and being greater than unity. The estimated effective dose for all the sites is between 0.11 ̶ 0.47 mSv/year over 1–27 years of exposure. The value for the cancer risk is in the range (6.51–10.3) × 10–4 for up to 15-year continuous operation at the sites. The study reveals that the artisanal miners are at risk, and appropriate remediation for all the sites is strongly recommended.